Chemistry Reference
In-Depth Information
Fig. 4.
Theoretical surface divergence for a 15 Hz capillarygravity wave. Curves
are shown for an ideal inviscid flow, a real flow with zero viscoelasticity, and a
surfactant flow with a finite viscoelasticity. Each curve is along the phase of each
wave, with the horizontal position at zero corresponding to a wave crest. The
wave amplitude : wavelength ratio is 1 : 20
Next, we report results of a laboratory investigation focused on the ef-
fects of surface films on the flow field near the airҟ/water interface. For re-
peatability and simplicity, we selected an axisymmetric vortex ring for the
source of surface expansion and dilation (divergences) of the near surface.
A detailed description of the experimental apparatus can be found in
McKenna (1997). In summary, the technique relied on forcing a small slug
of fluid from the mouth of a knife-edged stainless steel tube vertically into
a visualisation tank. Upon exit from the tube orifice, the fluid rolled up
into a vortex ring and propagated upward where it then interacted with the
free surface. Surfaces with varying surfactant concentration were used to
examine the influence of different surfactant composition on ring impact
and the ensuing hydrodynamics. Shown in Fig. 5 are flow visualisation re-
sults taken from McKenna (1997) illustrating the effect of surfactants on
the near-surface flow field. Four cases are presented: (a) approach toward
a free surface, (b) interaction with a nominally clean free surface, (c) inter-
action with a surface covered with a microlayer of stearic acid, and (d) in-
teraction with a solid wall boundary.
